If you use Google Authenticator or a similar app to generate 2-step verification codes, and no longer have access to your device, you can restore this ability to another device if you saved the secret seed provided when setting up your 2-step verification device. You may have written down this secret seed or saved it to a USB drive.
If you've lost your authentication device and do not have access to the secret seed, please refer to this page for recovery steps.
Originally, to start generating codes you would have scanned a QR code with your phone. The following steps will show you how to generate these codes from only the secret seed for several apps:
Google Authenticator
When you open the app, add a new seed by selecting the red plus in the bottom right corner. Select Enter a provided key from the menu that appears.
In the form, fill out the account name with something that describes this account (such as "Coinbase") and type the seed into the field for the key.
DUO
Click the add key button in the top right corner of the screen. In the next screen (QR code scanner) click the no barcode button. From there, you can select Coinbase. Enter your Coinbase account email and the Coinbase secret seed in the Account and Key fields.